The goal of the Eye Disorders Case Control Study (EDCCS) is to identify potential risk factors for several disorders of the eye for which adequate epidemiologic data are now lacking. To accomplish this goal, four clinical centers have been selected to participate in the study. The clinical centers are located in Boston, New York, Chicago, and Milwaukee. The Data Center is located in Bethesda, Maryland. Two biochemistry laboratories are also participating: CDC in Atlanta and National Health Laboratories in Vienna, Virginia. The EDCCS Reading Center, located in Boston, is responsible for developing grading systems for evaluating the fundus photographs, grading the fundus photographs and angiograms, submitting their evaluations to the Data Center, and collaborating in the preparation of manuscripts.